The present invention relates to a transfer flat type ball grid array (TF-BGA) method for manufacturing a packaging substrate, which is totally different from a conventional BGA method for manufacturing a packaging substrate. This method has advantages of: forming fine circuitry; improving electrical performance; reducing a waste material and therefore reducing the ultimate cost as well, reducing harm to the environment, improving the heat dissipation efficiency; and improving the yield due to salvaging some reusable substrate units from semi-scraped strip of substrate set.
A conventional BGA method for manufacturing a packaging substrate comprises sequential steps shown in FIG. 3A through FIG. 3H. First, FIG. 3A shows a step of drilling a double-sided laminate 70 with two layers of copper foils 71 on opposite sides thereof to form via holes 711. Next, FIG. 3B shows a step of plating the via holes 711 with copper 72 to form a connection between the two layers of copper foils 71. Then, FIG. 3C shows a step of applying a layer of etching resist (dry film) 73 on the copper foils 71 layers for forming circuit patterns. Subsequently, FIG. 3D shows a step of applying a layer of solder resist 75 on predetermined areas on both sides after the circuit patterns 74 having been formed on the laminate 70. Thereafter, FIG. 3E shows a step of filling up the via holes 711 with conductive paste 76 and attaching a die 77 thereon for performing functions of heat dissipation and die attachment. Then, FIGS. 3F, 3G and 3H sequentially proceed steps of bonding gold wires 78 between the die 77 and the circuit patterns 74, providing a mold tool for covering a bonding area with molding compound 79 and attaching solder balls 80 on ball pads defined by solder resist 75 through soldering.
Based on a conventional operating process, a plurality of packaging substrate units in a long strip form as shown in FIG. 2 for use in automatic machinery is produced through a commonly used packaging operation.
However, the packaging substrate units being made in a long strip form by using the conventional BGA method described above have several drawbacks which are as follows:
(1) Since the conventional BGA method adopts a double-sided circuit design, a complicate drilling step has to be taken and insufficient accuracy in via holes filling may create concern about reliability. PA1 (2) The efficiency of heat dissipation through via holes is not effective and the step of filling up the via holes with conductive paste still has a potential reliability problem. PA1 (3) In the conventional BGA method, since the die is attached on the conductive paste and covered by molding compound, a mold tool has to be provided for filling in the molding compound. Therefore, this assembly process lacks flexibility. PA1 (4) The electrical performance is hard to improve since a grounding layer can not be easily added. PA1 (5) A high-density circuitry is hard to achieve since via holes occupy some space in accordance with the drilling process. PA1 (6) When one or two packaging substrate units in a long strip are scraped, the entire strip has to be scraped. This will lead to wasting material and lowering the yield, and doing harm to the environment.
In view of employing a double-sided circuit board and the conventional BGA method described above, there are several defects such as the complicated manufacturing, the electrical performance, etc., of the packaging process as well as a poor yield and poor usage of material due to the design in a long strip form, all of which have to be overcome.